1. Field of the Invention
The present invention relates to a magnetic optical member used in an optical isolator and an optical magnetic recording medium and the like, and to a method of producing the same.
2. Description of the Related Art
An optical isolator used in optical fiber communication systems generally includes, for example, a pair of polarizers and a Faraday rotator interposed between the pair of polarizers. The Faraday rotator has the Faraday effect (magneto-optical effect) and rotates a polarizing surface of incident light by 45 degrees, that is the Faraday rotational angle is set to 45 degrees.
Recently, in addition to the optical isolator, an optical device utilizing the above-mentioned magneto-optical effect (hereinafter referred to as magnetic optical member), such as an optical magnetic recording medium (an optical magnetic disk) and an optical switch has been greatly used.
In recording of optical magnetic recording using, for example, an optical magnetic recording medium (an optical magnetic disk), temperature of the optical magnetic recording medium is locally increased by irradiation with laser light and recording is made with an external magnetic field only in the local portion where coercive force was decreased by the temperature increase. Since the spot diameter of the laser light can be reduced to about its wavelength, that is, a submicron length or so by narrowing the light with a lens, high density recording can be performed when combined with a vertically magnetized film as a recording medium.
The reproduction of information recorded on the optical magnetic recording medium utilizes the principle (Kerr effect) that when an optical magnetic recording medium is irradiated with linearly polarized laser light, rotation is made in mutually opposite directions depending on the direction of the polarizing surface to the reflected light, that is, depending on whether the direction is upward or downward with respect to the vertical direction to the film surface. On the optical magnetic recording medium (an optical magnetic disk), a laser light guiding groove is formed into a spiral shape so that minute recording bits can be correctly recorded and reproduced. The reproducing device (optical magnetic disk drive) is provided with an automatic focusing mechanism and an automatic tracking mechanism for tracking the laser light along the groove in the optical system (pick-up head).
Further, recently high densification has been required for the optical magnetic recording medium, and development of a blue color laser for narrowing the laser light has been attempted. In this case, an optical magnetic recording medium (magnetic optical member) having a large Kerr rotational angle for short wavelength laser light is required. Since rare earth iron garnet based materials, for example, bismuth-substituted rare earth iron-garnet (BiYIG) and the like have a large Kerr rotation (magneto-optical effect) at the short wavelength, even if the recording spot diameter, that is, the recording area is reduced, a large signal can be obtained. Thus, to form a magnetic optical member using BiYIG with a large magneto-optical effect is considered.
Incidentally, the crystal structure of the BiYIG is amorphous just after the film formation, and annealing treatment to enhance crystallinity at 600xc2x0 C. or more is needed for obtaining large Hc (and excellent magnetic optical characteristics). On the other hand, the optical magnetic recording medium is generally placed on a resin substrate, which is deformed by the above-mentioned heat treatment. Therefore, under the above circumstances, it is difficult to form the optical magnetic recording medium using a rare earth iron garnet based magnetic material, and an excellent magneto-optical effect that the rare earth iron garnet based material possesses cannot be utilized.
Incidentally, it is thinkable that glass is used as the substrate. However, a glass substrate is difficult to form a guiding groove for laser light. Therefore, the use of the glass was not effective as the solution of the above-mentioned problems.
The present invention has been made in view of the above-mentioned circumstances and, therefore, an object of the present invention is to provide a magnetic optical member that can obtain a large magneto-optical effect using a rare earth iron garnet based material, and a method of producing the same.
According to a first aspect of the present invention, a magnetic optical member is characterized by comprising a polymeric substrate on which a magnetic optical thin film made of crystalline rare earth iron garnet is formed.
According to a second aspect of the present invention, the magnetic optical member in the first aspect of the present invention is characterized in that there are provided two dielectric multi-layer films in which plural kinds of dielectric materials having different optical characteristics are alternately laminated with regularity in thickness, and in that the magnetic optical thin film is placed between the two dielectric multi-layer films.
According to a third aspect of the present invention, the magnetic optical member in the first or second aspect of the present invention is characterized in that the polymeric substrate is a thermoplastic resin substrate.
According to a fourth aspect of the present invention, the magnetic optical member in any one of the first to third aspects of the present invention is characterized in that the polymeric substrate is a tape-shaped, film-shaped, or sheet-shaped substrate.
According to a fifth aspect of the present invention, the magnetic optical member in any one of the first to fourth aspects of the present invention is characterized in that the magnetic optical thin film is capable of magnetic recording.
According to a sixth aspect of the present invention, a method of producing a magnetic optical member comprising: two dielectric multi-layer films in which plural kinds of dielectric materials having different optical characteristics are alternately laminated with regularity in thickness; a magnetic optical thin film of rare earth iron-garnet, placed between the two dielectric multi-layers; and a polymeric substrate on which the layers and film are formed, is characterized in that the magnetic optical thin film is crystallized without deforming the polymeric substrate by the pulse heating wherein infrared beam is intermittently irradiated.
According to a seventh aspect of the present invention, the method of producing a magnetic optical member in the sixth aspect of the present invention is characterized in that the magnetic optical thin film is heated without disordering the cyclic structure of the dielectric multi-layer films.
According to an eighth aspect of the present invention, the method of producing a magnetic optical member in the sixth or seventh aspect of the present invention is characterized in that the polymeric substrate is cooled during heating the magnetic optical thin film.
According to a ninth aspect of the present invention, the method of producing a magnetic optical member in the sixth aspect of the present invention is characterized by using, in place of the infrared beam, laser light having a wavelength with which the light is not absorbed in the polymeric substrate but is absorbed in the magnetic optical thin film.
According to a tenth aspect of the present invention, the method of producing a magnetic optical member in the ninth aspect of the present invention is characterized in that the laser light has a wavelength with which the light is not absorbed in the dielectric multi-layer film.
According to an eleventh aspect of the present invention, the method of producing a magnetic optical member in the tenth aspect of the present invention is characterized in that scanning with the laser light is performed.
According to a twelfth aspect of the present invention, the method of producing a magnetic optical member in any one of the sixth to eleventh aspects of the present invention is characterized in that the polymeric substrate is a thermoplastic resin substrate.
According to a thirteenth aspect of the present invention, the method of producing a magnetic optical member in any one of the sixth to twelfth aspects of the present invention is characterized in that the polymeric substrate is a tape-shaped, film-shaped, or sheet-shaped substrate.
According to a fourteenth aspect of the present invention, the method of producing a magnetic optical member in any one of the sixth to thirteenth aspects of the present invention is characterized in that the magnetic optical thin film is capable of magnetic recording.